As various electronic devices have been reduced in weight due to a reduction in size, a wireless power charging scheme for charging a battery using magnetic coupling (or inductive coupling) without electrical contact has come into prominence.
A wireless power charging scheme is a scheme in which charging is performed through the use of electromagnetic induction. A primary coil (transmitter coil) is provided in a charger (wireless power transmitting device), a secondary coil (receiver coil) is provided in a charge target (wireless power receiving device), and a current is generated according to inductive coupling between the primary coil and the secondary coil. This current provides energy used to charge a battery.
A sheet for shielding against electromagnetic waves (or a shielding sheet) is disposed between the receiver coil and the battery. The shielding sheet serves to block a magnetic field generated by the receiver coil from reaching the battery and to allow electromagnetic waves generated by the wireless power transmitting device to be effectively transmitted to the wireless power receiving device.
In the sheet for shielding against electromagnetic waves, an eddy current may be generated due to electromotive force resulting from a change in magnetic flux within a magnetic material. The eddy current may cause power loss and an increase in temperature of the magnetic material. Also, a magnetic field generated by the eddy current may inversely act on a direction of a magnetic field generated by the transmitter, significantly degrading charging efficiency.